Caffeine and nicotine acutely inhibit flow-mediated vasodilation, but not both are necessarily harmful in the long term.

Today, flow-mediated dilation (FMD) is a standardized test for the non-invasive assessment of vascular endothelial function in humans. The test is often used to assess the influence of various living conditions on the vascular system. Many factors have a short-term effect on FMD and reduce it. However, not every short-term FMD-reducing effect also signals long-term vascular damage with repeated exposure. The comparison between coffee consumption and smoking will be used to discuss that although both stimulants lead to comparable acute changes in vascular function, they differ in their long-term effects on the vascular system. Therefore, acute FMD effects cannot always be equated with long-term damaging effects.